The use of biomaterials, e.g. restorative materials, in both the dental and medical fields is widespread and there is a high demand for products in this area. Restorative materials, e.g. amalgam or resin composites, are used extensively to repair dental tissues and bones.
In the dental field, there has been a focus on improving the adhesion of resins to hard tissue, e.g., dentin or enamel. The adhesives typically are used after pretreating or etching the hard tissue with an acid, e.g., maleic, phosphoric, or citric. New resin composites are continually being developed and marketed. Some of these composites are designed to achieve higher bond strengths or improve physical properties and esthetics of the restored target substrate. Other goals in the design of these composites are related to their use and include reducing operating time and formulating for simpler use or use under relatively humid conditions (see Titley et al. American Journal of Dentistry, Vol. 7, No. 4, (August 1994)).
Bonding systems typically used in the dental field remove the smear layer and demineralize the surface of the dental tissue by acid etching. The systems also can use priming agents, e.g., to alter wettability or chemical reactivity of the pretreated dentin, prior to applying a bonding agent, e.g., a polymerizable monomer. Following polymerization, the bonding agent bonds to the dentin in a manner which is not entirely understood (chemically, mechanically, interfacial diffusion or a combination thereof) by those skilled in the art. After the application of bonding systems and their polymerization, an approximately 5 micron thick hybrid layer is formed which is part resin and part dentin. This hybrid layer has been studied with an emphasis on its composition and the importance of the depth and effectiveness of the penetration of the bonding agent. (see Titley et al. American Journal of Dentistry, cited supra). The layer is believed to contain little or no apatite and the adhesion to dentin is believed to occur through the investment of collagen with the bonding agent. Until recently, it was difficult to study the interactions occurring in the hybrid layer because the collagen-bonding agent combinations were not clearly demonstrated.
Even though there has been focus in this area, presently available techniques and/or products for pretreating the dental tissue or adhering the restorative materials to the dental tissue have limitations. The clinical requirements of the bonds are known in that the bonding agents should effectively seal the dentin tubules to prevent post operative sensitivity and protect the pulp and the bonds should last the lifetime of the restoration and be durable under a variety of conditions. Those skilled in the art have encountered difficulties in achieving these requirements. This is partly due to the fact that the mechanism of the bonding of resin composites to the hard tissues is not entirely understood.